Extra doped region for back-side deep trench isolation

ABSTRACT

The present disclosure, in some embodiments, relates to a method of forming an image sensor. The method includes implanting a dopant into a substrate to form a doped region and implanting one or more additional dopants into the substrate to form an image sensing element between the doped region and a front-side of the substrate. The doped region directly contacts a boundary of the image sensing element that is furthest from the front-side of the substrate. The method further includes etching the substrate to form one or more trenches extending into a back-side of the substrate. The back-side of the substrate opposes the front-side of the substrate. The method further includes filling the one or more trenches with one or more dielectric materials to form isolation structures.

REFERENCE TO RELATED APPLICATION

This Application is a Divisional of U.S. application Ser. No. 15/919,784, filed on Mar. 13, 2018, which is a Continuation of U.S. application Ser. No. 14/923,635 filed on Oct. 27, 2015 (now U.S. Pat. No. 9,954,022, issued on Apr. 24, 2018). The contents of the above-referenced matters are hereby incorporated by reference in their entirety.

BACKGROUND

Digital cameras and optical imaging devices employ image sensors. Image sensors convert optical images to digital data that may be represented as digital images. An image sensor typically includes an array of pixel sensors, which are unit devices for the conversion of an optical image into electrical signals. Pixel sensors often manifest as charge-coupled devices (CCDs) or complementary metal oxide semiconductor (CMOS) devices. However, CMOS pixel sensors have recently received more attention. Relative to CCD pixel sensors, CMOS pixel sensors provide lower power consumption, smaller size, and faster data processing. Further, CMOS pixel sensors provide a direct digital output of data, and generally have a lower manufacturing cost compared with CCD pixel sensors.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 illustrates a cross-sectional view of some embodiments of a CMOS (complementary metal-oxide-semiconductor) image sensor having a light sensing element separated from a deep trench isolation (DTI) structure by a doped region.

FIG. 2 illustrates a cross-sectional view of some embodiments of an integrated chip comprising a photodiode separated from a back-side deep trench isolation (BDTI) structure by a doped region.

FIG. 3 illustrates a cross-sectional view of some additional embodiments of a BSI-CMOS image sensor comprising a photodiode separated from a BDTI structure by a p-type doped region.

FIGS. 4-11 illustrate some embodiments of cross-sectional views showing a method of forming a CMOS-BSI image sensor having a doped region separating a photodiode and a BDTI structure.

FIG. 12 illustrates a flow diagram of some embodiments of a method of forming a CMOS-BSI image sensor having a doped region separating an image sensing element from a BDTI structure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

Many portable electronic devices (e.g., cameras, cellular telephones, computers, etc.) include an image sensor for capturing images. One example of such an image sensor is a CMOS image sensor (CIS) including an array of active pixel sensors (APSs). Deep trench isolation (DTI) structures are often arranged between adjacent pixels of a CIS to isolate neighboring pixels. These DTI structures are formed by using an etch process to form a deep trench within the semiconductor substrate, which is then filled with an insulating material. In some applications, a functional layer is disposed over an upper surface of the semiconductor substrate prior to etching the deep trench. The functional layer can enhance the performance of the semiconductor device, but also comprises one or more potential contaminants for the substrate.

In some instances, the etch process used to form the deep trench dissociates these contaminants from the functional layer, and the dissociated contaminants then diffuse into the semiconductor substrate through sidewalls of the deep trench as the deep trench is being formed. These contaminants can degrade performance CIS by introducing interface defects near an edge of the DTI structure. The interface defects can lead to an increase in dark current and/or white pixel number. The increase in dark current causes charges to accumulate even when light is not impingent on the image sensors, thereby becoming a major source of noise that can degrade image quality of digital imaging devices.

The present disclosure relates to a CMOS image sensor comprising a doped region, arranged between deep trench isolation structures and an image sensing element, which is configured to reduce dark current and white pixel number, and an associated method of formation. In some embodiments, the CMOS image sensor has a pixel region disposed within a semiconductor substrate. The pixel region has an image sensing element configured to convert radiation into an electric signal. A plurality of back-side deep trench isolation (BDTI) structures extend into the semiconductor substrate on opposing sides of the pixel region. A doped region is laterally arranged between the BDTI structures and separates the image sensing element from the BDTI structures and the back-side of the semiconductor substrate. Separating the image sensing element from the BDTI structures prevents the image sensing element from interacting with interface defects near edges of the BDTI structures, and thereby effectively reduces dark current and improves white pixel number performance without any adverse side-effect.

FIG. 1 illustrates a cross-sectional view of some embodiments of a CMOS (complementary metal-oxide-semiconductor) image sensor 100 having a light sensing element separated from a deep trench isolation (DTI) structure by a doped region.

The CMOS image sensor 100 comprises a semiconductor substrate 102 having a plurality of pixel regions 103 a-103 c. The plurality of pixel regions 103 a-103 c respectively comprise an image sensing element 104 configured to convert incident radiation 120 (e.g., photons) into an electric signal. In some embodiments, the image sensing element 104 may comprise a photodiode. In such embodiments, the photodiode may comprise a first region within the semiconductor substrate 102 having a first doping type (e.g., n-type doping) and an adjoining second region within the semiconductor substrate 102 having a second doping type (e.g., p-type doping) that is different than the first doping type. In some embodiments, the plurality of pixel regions 103 a-103 c may be arranged within the semiconductor substrate 102 in an array comprising rows and/or columns.

The pixel regions 103 a-103 c are isolated from adjacent pixel regions 103 a-103 c by deep trench isolation (DTI) structures 111 extending into the semiconductor substrate 102 and comprising one or more dielectric materials 112-114. In some embodiments, the one or more dielectric materials 112-114 may comprise a passivation layer 112 and a dielectric fill layer 114 (e.g., an oxide), for example. In some embodiments, the DTI structures 111 may comprise back-side deep trench isolation (BDTI) structures that vertically extend from a back-side of the semiconductor substrate 102 to a location within the semiconductor substrate 102. The back-side of the semiconductor substrate 102 opposes a back-end-of-the-line (BEOL) metallization stack comprising a plurality of metal interconnect layers 108 arranged within an ILD layer 106.

A plurality of color filters 116 are arranged over the back-side of the semiconductor substrate 102. The plurality of color filters 116 are respectively configured to transmit specific wavelengths of incident radiation 120. For example, a first color filter (e.g., a red color filter) may transmit light having wavelengths within a first range, while a second color filter may transmit light having wavelengths within a second range different than the first range. A plurality of micro-lenses 118 are arranged over the plurality of color filters 116. Respective micro-lenses 118 are aligned laterally with the color filters 116 and overlie the pixel regions 103 a-103 c. The micro-lenses 118 are configured to focus the incident radiation 120 (e.g., light) towards the pixel regions 103 a-103 c.

A doped region 110 is arranged along a surface of the pixel regions 103 a-103 c opposing at a location that is between the pixel regions 103 a-103 c and the plurality of color filters 116. The doped region 110 separates the image sensing elements 104 within the pixel regions 103 a-103 c from the DTI structures 111. The doped region 110 has a greater concentration of dopants than the pixel region 103 a-103 c. In some embodiments, the doped region 110 may comprise a p-type region, while in other embodiments the doped region 110 may comprise an n-type region. The greater doping concentration of the doped region 110 forms a region that separates the image sensing element 104 from interface defects located along the edges of the DTI structures 111, and thereby reduces the dark current and/or white pixel number of the CMOS image sensor 100.

FIG. 2 illustrates a cross-sectional view of some embodiments of an integrated chip 200 comprising a photodiode 202 separated from a back-side deep trench isolation (BDTI) structure by a doped region.

The photodiode 202 comprises a first region 202 a and an underlying second region 202 b arranged within the semiconductor substrate 102. The first region 202 a has a first doping type and the second region 202 b has a second doping type that is different than the first doping type. In some embodiments, the first region 202 a comprises an n-type region and the second region 202 b comprises a p-type region.

A plurality of BDTI structures 204 a-204 b are arranged within a back-side 102 b of the semiconductor substrate 102 and extend from the back-side 102 b of the semiconductor substrate 102 to a position laterally separated from the photodiode 202. The plurality of BDTI structures comprise one or more dielectric materials 112-114 arranged within a trench in the semiconductor substrate 102. In various embodiments, the plurality of BDTI structures 204 a-204 b may extend to a depth d_(BDTI) of greater than or equal to approximately 0.5 microns within the semiconductor substrate 102.

A doped region 110 is vertically arranged between the photodiode 202 and the back-side 102 b of the semiconductor substrate 102. The doped region 110 has an opposite doping type as the first region 202 a of the photodiode 202 so that the doped region 110 separates the photodiode 202 from the plurality of BDTI structures 204 a-204 b. For example, in some embodiments, the first region 202 a may comprise an n-type doping, while the doped region 110 may comprise a p-type region. In other embodiments, the first region 202 a may comprise a p-type doping, while the doped region 110 may comprise an n-type region.

The photodiode 202 may vertically extend to a position that abuts the doped region 110. In some embodiments, the doped region 110 may be arranged along sidewalls of the photodiode 202, so that the doped region 110 laterally separates the first region 202 a of the photodiode 202 from the plurality of BDTI structures 204 a-204 b and vertically separates the first region 202 a from one or more dielectric materials 112-114 overlying the back-side 102 b of the semiconductor substrate 102. The doped region 110 laterally extends between sidewalls of the plurality of BDTI structures 204 a-204 b. For example, the doped region 110 laterally extends from a sidewall of a first BDTI structure 204 a to a sidewall of a second BDTI structure 204 b.

In some embodiments, the doped region 110 may have a doping concentration that is greater than or equal to approximately 5e15 dopants/cm³. In some additional embodiments, the doped region 110 may have a doping concentration that is greater than or equal to approximately 1e17 dopants/cm³. The doped region 110 has a depth d_(P) that is less than the depth d_(BDTI) of the plurality of BDTI structures 204 a-204 b, such that the plurality of BDTI structures 204 a-204 b vertically extend through the doped region 110. For example, in various embodiments, the doped region 110 may extend to a depth d_(P) of greater than or equal to approximately 0.1 microns within the semiconductor substrate 102.

FIG. 3 illustrate cross-sectional views of some additional embodiments of a back-side illumination CMOS (BSI-CMOS) image sensor 300 comprising a photodiode separated from a back-side deep trench isolation (BDTI) structure by a p-type doped region.

The BSI-CMOS image sensor 300 comprises a pixel region 301 arranged within a semiconductor substrate 102. In some embodiments, the pixel region 301 may be isolated from adjacent pixel regions by one or more isolation structures 306 (e.g., shallow trench isolation regions) arranged within the semiconductor substrate 102 on opposing sides of the pixel region 301. The one or more isolation structures 306 may comprise an insulating material arranged within a trench in a front-side 102 f of the semiconductor substrate 102.

The pixel region 301 comprises a photodiode 302 having a first region 302 a with a first doping type (e.g., n-type doping) and a second region 302 b with a second doping type (e.g., p-type doping) that is different than the first doping type. The first region 302 a vertically extends from the second region 302 b to a p-type region 303. In some embodiments, the p-type region 303 may have a doping concentration greater than or equal to approximately 5e15 atoms/cm³. In some embodiments, the p-type region 303 may be arranged along a back-side 102 b of the semiconductor substrate 102.

A transfer transistor 309 is arranged over the front-side 102 f of the semiconductor substrate 102. The transfer transistor 309 comprises a gate dielectric layer 308 is disposed over the front-side of the semiconductor substrate 102 and a gate electrode 310 is arranged onto the gate dielectric layer 308. In some embodiments, sidewall spacers 312 are arranged on opposing sides of the gate electrode 310. The transfer transistor 309 is laterally arranged between the photodiode 302 and a floating diffusion well 304.

An ILD layer 106 is arranged along the front-side 102 f of the semiconductor substrate 102. The ILD layer 106 comprises one or more ILD materials. In various embodiments, the ILD layer 106 may comprise one or more of a low-k dielectric layer (i.e., a dielectric with a dielectric constant less than about 3.9), an ultra low-k dielectric layer, or an oxide (e.g., silicon oxide). Conductive contacts 314 are arranged within the ILD layer 106. The conductive contacts 314 extend from the gate electrode 310 and the floating diffusion well 304 to one or more metal wire layers (not shown). In various embodiments, the conductive contacts 314 may comprise a conductive metal such as copper or tungsten, for example.

Back-side deep trench isolation (BDTI) structures 315 are arranged within the back-side 102 b of the semiconductor substrate 102 along edges of the pixel region 301. The plurality of BDTI structures 315 may comprise a passivation layer 316 arranged onto sidewalls of a trench extending into the back-side 102 b of the semiconductor substrate 102. A high-k dielectric layer 318 vertically and laterally separates the passivation layer 316 from a dielectric fill layer 114 that fills in a remainder of the trench. In some embodiments, the passivation layer 316 and the high-k dielectric layer 318 may extend over the back-side 102 b of the semiconductor substrate 102 between a first trench and the second trench. In some embodiments, the passivation layer 316 may comprise an anti-reflective coating (ARC), such as a bottom resist anti-reflective coating (BARC), for example. In other embodiments, the passivation layer 316 may comprise an organic polymer or a metallic oxide. In some embodiments, the high-k dielectric layer 318 may comprise hafnium oxide (HfO), hafnium silicon oxide (HfSiO), hafnium aluminum oxide (HfAlO), or hafnium tantalum oxide (HfTaO), for example.

A layer of dielectric material 320 vertically separates a plurality of color filters 116 from the back-side 102 b of the semiconductor substrate 102. In some embodiments, the plurality of color filters 116 may be arranged within a grid structure 322 disposed onto the layer of dielectric material 320. In some embodiments, the grid structure 322 may comprise a stacked grid having a metal framework surrounded by a dielectric material. In some embodiments, layer of dielectric material 320 and the stacked grid may have a same dielectric material (e.g., silicon-dioxide (SiO₂)).

A plurality of micro-lenses 118 are arranged over the plurality of color filters 116. In some embodiments, the plurality of micro-lenses 118 have a substantially flat bottom surface abutting the plurality of color filters 116 and a curved upper surface. The curved upper surface is configured to focus incident radiation towards the underlying pixel region 301.

During operation of the BSI-CMOS image sensor 300 incident radiation is focused by the micro-lens 118 to the underlying pixel region 301. When incident radiation of sufficient energy strikes the photodiode 302, it generates an electron-hole pair that produces a photocurrent. The transfer transistor 309 controls charge transfer from the photodiode 302 to the floating diffusion well 304. If the charge level is sufficiently high within the floating diffusion well 304, a source follower transistor 324 is activated and charges are selectively output according to operation of a row select transistor 326 used for addressing. A reset transistor 328 is configured to reset the photodiode 302 between exposure periods.

FIGS. 4-11 illustrate some embodiments of cross-sectional views 400-1100 showing a method of forming a CMOS-BSI image sensor having doped region separating a photodiode from a back-side deep trench isolation (BDTI) structure.

As shown in cross-sectional view 400 of FIG. 4, a dopant species 404 is implanted into a semiconductor substrate 402 to form a doped region 406. In various embodiments, the semiconductor substrate 402 may comprise any type of semiconductor body (e.g., silicon/CMOS bulk, SiGe, SOI, etc.) such as a semiconductor wafer or one or more die on a wafer, as well as any other type of semiconductor and/or epitaxial layers formed thereon and/or otherwise associated therewith. In some embodiments, the dopant species 404 may comprise a p-type dopant (e.g., boron) that is implanted into a front-side 402 f of the semiconductor substrate 402. In other embodiments, the dopant species 404 may comprise an n-type dopant (e.g., phosphorous). In some embodiments, the dopant species 404 may be implanted into the back-side 402 b of the semiconductor substrate 402. In some embodiments, the dopant species 404 may be implanted as a blanket implantation (i.e., an unmasked implantation). In other embodiments, the dopant species 404 may be implanted as a selective implantation (i.e., a masked implantation).

As shown in cross-sectional view 500 of FIG. 5, a transfer transistor 309 is formed over a front-side 402 f of the semiconductor substrate 402. The transfer transistor 309 may be formed by depositing a gate dielectric film and a gate electrode film over the semiconductor substrate 402. The gate dielectric film and the gate electrode film are subsequently patterned to form a gate dielectric layer 308 and a gate electrode 310. Sidewall spacers 312 may be formed on the outer sidewalls of the gate electrode 310. In some embodiments, the sidewall spacers 312 may be formed by depositing nitride onto the front-side 402 f of the semiconductor substrate 402 and selectively etching the nitride to form the sidewall spacers 312.

Implantation processes are performed within the front-side 402 f of the semiconductor substrate 402 to form a photodiode 302 along a first side of the transfer transistor 309 and a floating diffusion well 304 along an opposite, second side of the transfer transistor 309. The photodiode 302 may be formed by selectively implanting the semiconductor substrate 102 with a first implantation process to form a first region 302 a having a first doping type (e.g., n-type), and a second subsequent implantation process to form an abutting second region 302 b having a second doping type (e.g., p-type) different than the first doping type. In some embodiments, the first region 302 a may vertically abut the doped region 406. In some embodiments, the semiconductor substrate 402 may be selectively implanted according to a patterned masking layer (not shown) comprising photoresist.

In some embodiments, one or more isolation structures 306 (e.g., shallow trench isolation regions) may be formed within the front-side 402 f of the semiconductor substrate 402 on opposing sides of a pixel region 301. The one or more isolation structures 306 may be formed by selectively etching the front-side 402 f of the semiconductor substrate 402 to form shallow-trenches and subsequently forming an oxide within the shallow-trenches. In some embodiments, the one or more isolation structures 306 may be formed prior to formation of the transfer transistor 309, the photodiode 302, and/or the floating diffusion well 304.

As shown in cross-sectional view 600 of FIG. 6, a BEOL metallization stack comprising a plurality of metal interconnect layers 108 arranged within an ILD layer 106 is formed over the front-side 402 f of the semiconductor substrate 402. In some embodiments, the BEOL metallization stack may be formed by forming the ILD layer 106, which comprises one or more layers of ILD material, over the front-side 402 f of the semiconductor substrate 402. The ILD layer 106 is subsequently etched to form via holes and/or metal trenches. The via holes and/or metal trenches are then filled with a conductive material to form the plurality of metal interconnect layers 108. In some embodiments, the ILD layer 106 may be deposited by a physical vapor deposition technique (e.g., PVD, CVD, etc.). The plurality of metal interconnect layers 108 may be formed using a deposition process and/or a plating process (e.g., electroplating, electro-less plating, etc.). In various embodiments, the plurality of metal interconnect layers 108 may comprise tungsten, copper, or aluminum copper, for example.

As shown in cross-sectional view 700 of FIG. 7, the ILD layer 106 is bonded to a handle substrate 702. In some embodiments, the bonding process may use an intermediate bonding oxide layer (not shown) arranged between the ILD layer 106 and the handle substrate 702. In some embodiments, the bonding process may comprise a fusion bonding process. In some embodiments, the handle substrate 702 may comprise a silicon wafer.

As shown in cross-sectional view 800 of FIG. 8, a thickness of the semiconductor substrate 102 is reduced. Thinning the semiconductor substrate 102 reduces a thickness of the substrate from a first thickness t₁ to a second thickness t₂ to allow for radiation to pass through the back-side 102 b of the semiconductor substrate 102 to the photodiode 302. In some embodiments, the semiconductor substrate 102 may be thinned by etching the back-side 402 b of the semiconductor substrate. In other embodiments, the semiconductor substrate 102 may be thinned by mechanical grinding the back-side 402 b of the semiconductor substrate.

As shown in cross-sectional view 900 of FIG. 9, the semiconductor substrate 102 is selectively etched to form deep trenches 902 a-902 b within the back-side 102 b of the semiconductor substrate 102. In some embodiments, the semiconductor substrate 102 may be etched by forming a masking layer 904 onto the back-side 102 b of the semiconductor substrate 102. The semiconductor substrate 102 is then exposed to an etchant 906 in regions not covered by the masking layer 904. The etchant 906 etches the semiconductor substrate 102 to form deep trenches 902 a-902 b extending to the semiconductor substrate 102. The deep trenches 902 a-902 b extend through the doped region 110 to a position within the semiconductor substrate 102 that is laterally separated from the photodiode 302 by the doped region 110.

In various embodiments, the masking layer 904 may comprise photoresist or a nitride (e.g., SiN) patterned using a photolithography process. In various embodiments, the etchant 906 may comprise a dry etchant have an etching chemistry comprising a fluorine species (e.g., CF₄, CHF₃, C₄F₈, etc.) or a wet etchant (e.g., hydroflouric acid (HF) or Tetramethylammonium hydroxide (TMAH)).

As shown in cross-sectional view 1000 of FIG. 10, the deep trenches 902 a-902 b are filled with dielectric material. In some embodiments, a passivation layer 316 is formed within the deep trenches 902 a-902 b and a high-k dielectric layer 318 is formed within the deep trenches 902 a-902 b onto the passivation layer 316. The passivation layer 316 and the high-k dielectric layer 318 line sidewalls and bottom surfaces of the deep trenches 902 a-902 b. In some embodiments, the passivation layer 316 and the high-k dielectric layer 318 may extend over the back-side 102 b of the semiconductor substrate 102 between a first deep trench 902 a and a second deep trench 902 b. A dielectric fill layer 114 is formed to fill a remainder of the deep trenches 902 a-902 b. In some embodiments, a planarization process is performed after forming the dielectric fill layer 114 to form a planar surface that extends along an upper surface of the high-k dielectric layer 318 and the dielectric fill layer 114. In some embodiments, the passivation layer 316, the high-k dielectric layer 318, and the dielectric fill layer 114 may be deposited using a physical vapor deposition technique.

As shown in cross-sectional view 1100 of FIG. 11, a plurality of color filters 116 are formed over the back-side 102 b of the semiconductor substrate 102. In some embodiments, the plurality of color filters 116 may be formed by forming a color filter layer and patterning the color filter layer. The color filter layer is formed of a material that allows for the transmission of radiation (e.g., light) having a specific range of wavelength, while blocking light of wavelengths outside of the specified range. Further, in some embodiments, the color filter layer is planarized subsequent to formation.

A plurality of micro-lenses 118 are formed over the plurality of color filters 116. In some embodiments, the plurality of micro-lenses 118 may be formed by depositing a micro-lens material above the plurality of color filters 116 (e.g., by a spin-on method or a deposition process). A micro-lens template (not shown) having a curved upper surface is patterned above the micro-lens material. In some embodiments, the micro-lens template may comprise a photoresist material exposed using a distributing exposing light dose (e.g., for a negative photoresist more light is exposed at a bottom of the curvature and less light is exposed at a top of the curvature), developed and baked to form a rounding shape. The plurality of micro-lenses 118 are then formed by selectively etching the micro-lens material according to the micro-lens template.

FIG. 12 illustrates a flow diagram of some additional embodiments of a method 1200 of forming a CMOS-BSI image sensor having a light sensing element separated from back-side deep trench isolation (BDTI) regions by a p-type region.

While disclosed method 1200 is illustrated and described herein as a series of acts or events, it will be appreciated that the illustrated ordering of such acts or events are not to be interpreted in a limiting sense. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. In addition, not all illustrated acts may be required to implement one or more aspects or embodiments of the description herein. Further, one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases

At 1202, a dopant species is implanted into a semiconductor substrate to form a doped region. In some embodiments, the implantation is performed into a front-side of the semiconductor substrate. In alternative embodiments, the implantation may be performed into a back-side of the semiconductor substrate. In some embodiments, the dopant species may comprise a p-type dopant. FIG. 4 illustrates a cross-sectional view corresponding to some embodiments corresponding to act 1202.

At 1204, an image sensing element is formed within the front-side of the semiconductor substrate. In some embodiments, the image sensing element may comprise a photodiode formed by implanting dopant species into the front-side of the semiconductor substrate. FIG. 5 illustrates a cross-sectional view corresponding to some embodiments corresponding to act 1204.

At 1206, a transfer transistor is formed along the front-side of the semiconductor substrate. FIG. 5 illustrates a cross-sectional view corresponding to some embodiments corresponding to act 1206.

At 1208, a floating diffusion well is formed within the front-side of the semiconductor substrate. FIG. 5 illustrates a cross-sectional view corresponding to some embodiments corresponding to act 1208.

At 1210, a BEOL metallization stack is formed over the transfer transistor on the front-side of the semiconductor substrate. FIG. 6 illustrates a cross-sectional view corresponding to some embodiments corresponding to act 1210.

At 1212, the BEOL metallization stack is bonded to a handle substrate. FIG. 7 illustrates a cross-sectional view corresponding to some embodiments corresponding to act 1212.

At 1214, the semiconductor substrate is thinned by removing material from a back-side of the semiconductor substrate. FIG. 8 illustrates a cross-sectional view corresponding to some embodiments corresponding to act 1214.

At 1216, the back-side of the semiconductor substrate is selectively etched to form deep trenches extending into the semiconductor substrate. FIG. 9 illustrates a cross-sectional view corresponding to some embodiments corresponding to act 1216.

At 1218, the deep trenches are filled with one or more dielectric materials to form back-side deep trench isolation (BDTI) structures separated from the image sensing element by the doped region. FIG. 10 illustrates a cross-sectional view corresponding to some embodiments corresponding to act 1218.

At 1220, color filters and micro-lenses are formed over the back-side of the semiconductor substrate. FIG. 11 illustrates a cross-sectional view corresponding to some embodiments corresponding to act 1220.

Therefore, the present disclosure relates to a CMOS image sensor comprising a doped region, arranged between deep trench isolation structures and an image sensing element, which is configured to reduce dark current and white pixel number, and an associated method of formation.

In some embodiments, the present disclosure relates to a CMOS image sensor. The image sensor comprises a pixel region disposed within a semiconductor substrate and comprising an image sensing element configured to convert radiation into an electrical signal. The image sensor further comprises a plurality of back-side deep trench isolation (BDTI) structures extending from a back-side of the semiconductor substrate to positions within the semiconductor substrate located on opposing sides of the pixel region. The image sensor further comprises a doped region laterally arranged between the plurality of BDTI structures and configured to separate the image sensing element from the plurality of BDTI structures.

In some embodiments, the present disclosure relates to a CMOS image sensor. The image sensor comprises a photodiode arranged within a semiconductor substrate, and a plurality of back-side deep trench isolation (BDTI) structures extending from a back-side of the semiconductor substrate to positions within the semiconductor substrate on opposing sides of the photodiode. The image sensor further comprises a doped region arranged along the back-side of the semiconductor substrate and configured to separate the photodiode from the plurality of BDTI structures. The image sensor further comprises a back-end-of-the-line (BEOL) metallization stack arranged on a front-side of the semiconductor substrate and comprising a plurality of metal interconnect layers arranged within an inter-level dielectric layer.

In yet other embodiments, the present disclosure relates to method of forming an image sensor. The method comprises implanting a dopant species into a semiconductor substrate to form a doped region, and forming an image sensing element within a front-side of the semiconductor substrate. The method further comprises etching the semiconductor substrate to form a plurality of deep trenches extending into a back-side of the semiconductor substrate, wherein the back-side of the semiconductor substrate opposes the front-side of the semiconductor substrate. The method further comprises filling the plurality of deep trenches with one or more dielectric materials to form back-side deep trench isolation (BDTI) structures that are separated from the image sensing element by the doped region.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A method of forming an image sensor, comprising: implanting a dopant into a substrate to form a doped region; implanting one or more additional dopants into the substrate to form an image sensing element between the doped region and a front-side of the substrate, wherein the doped region directly contacts a boundary of the image sensing element that is furthest from the front-side of the substrate; etching the substrate to form one or more trenches extending into a back-side of the substrate, wherein the back-side of the substrate opposes the front-side of the substrate; and filling the one or more trenches with one or more dielectric materials to form isolation structures.
 2. The method of claim 1, wherein the doped region is formed so as to be separated from opposing surfaces of the substrate by non-zero distances.
 3. The method of claim 2, further comprising: thinning the substrate to expose the doped region along the back-side of the substrate.
 4. The method of claim 1, wherein the one or more trenches extend completely through the doped region.
 5. The method of claim 1, further comprising: forming a plurality of conductive interconnect layers within one or more inter-level dielectric layers on the front-side of the substrate.
 6. The method of claim 1, wherein the dopant is implanted into the front-side of the substrate to form the doped region prior to etching the substrate to form the one or more trenches.
 7. The method of claim 1, wherein the doped region is separated from the one or more dielectric materials along a first direction and along a second direction that is perpendicular to the first direction.
 8. The method of claim 1, wherein the doped region extends laterally past opposing edges of the image sensing element and is arranged vertically between the image sensing element and the back-side of the substrate.
 9. The method of claim 1, wherein the image sensing element is between the front-side of the substrate and a top of the doped region that faces the front-side of the substrate.
 10. A method of forming an image sensor, comprising: implanting a dopant into a substrate to form a doped region; forming an image sensing element between the doped region and a front-side of the substrate; etching a back-side of the substrate to form one or more trenches extending completely through the doped region on opposing sides of the image sensing element, wherein the back-side of the substrate opposes the front-side of the substrate; and filling the one or more trenches with one or more dielectric materials.
 11. The method of claim 10, wherein the doped region extends laterally past opposing sides of the image sensing element.
 12. The method of claim 10, wherein the doped region physically contacts a boundary of the image sensing element that is nearest the back-side of the substrate.
 13. The method of claim 10, wherein a bottom of the image sensing element facing the back-side of the substrate has a first width and a top of the image sensing element facing the front-side of the substrate has a second width that is greater than the first width.
 14. The method of claim 10, wherein the image sensing element has a first doped region that has a first maximum width and a second doped region that has a second maximum width that is larger than the first maximum width, the second doped region is between the first doped region and the front-side of the substrate.
 15. The method of claim 10, wherein the dopant is implanted into the front-side of the substrate to form the doped region.
 16. A method of forming an image sensor, comprising: implanting a dopant into a substrate to form a doped region; forming an image sensing element between the doped region and a front-side of the substrate; thinning the substrate to expose the doped region along a back-side of the substrate opposing the front-side; etching the back-side of the substrate to form one or more trenches; and forming one or more dielectric materials within the one or more trenches.
 17. The method of claim 16, wherein the one or more trenches protrude outward past the doped region towards the front-side of the substrate.
 18. The method of claim 16, wherein the doped region physically contacts a boundary of the image sensing element facing the back-side of the substrate.
 19. The method of claim 16, wherein the back-side of the substrate is etched to form the one or more trenches after thinning the substrate.
 20. The method of claim 16, wherein the dopant is implanted into the front-side of the substrate to form the doped region. 